PLC is a medium for advanced metering infrastructure (AMI) which allows communication signals to be sent through an existing powerline, so new communication lines are not needed. Current and next generation narrow band PLC are multi-carrier based, such as orthogonal frequency division multiplexing (OFDM)-based in order to obtain high network throughput. OFDM uses multiple orthogonal subcarriers to transmit data over a plurality of frequency selective channels.
In PLC networks, the system has the ability to communicate in both low voltage (LV) powerlines as well as high voltage power lines. When operating in a high-voltage powerline the system is able to communicate with low-voltage powerlines. This means that the receiver on the LV side must be able to detect the transmitted signal after it has been severely attenuated as a result of going through a medium voltage (MV)/LV transformer. The coupling interface between the PLC device and the MV medium may be referred to as a MV/LV crossing.
In PLC networks that have MV/LV crossings, data transmission over the full FCC allowed frequency band may not be feasible due to network conditions (e.g., noise) so that smaller frequency band portions referred to as tone masks (or simply tones), or groups of tones known as subbands, may be used for each particular MV/LV communication link. A tone map generally refers to an allocation of power for a subband comprising two or more tones.
Since the set of tones that provide effective communications for a particular link may vary link-to-link, and as a function of time, the receiver may not be tuned to the proper set of tones to decode the received frame. When nodes are unable to decode the data payload sent over the tones indicated in the received frame, such as indicated in the PHY header referred to as the frame control header (FCH) in the case of the IEEE P1901.2 standard (IEEE P1901.2), the node will set their virtual carrier sensing (VCS) to the Extended Interframe Space (EIFS) value to account for the largest data payload size transmission allowed in the PLC network.
Multi-Tone Mask (MTM) mode (or “tone masking”) refers to the use of multiple tone-masks/subbands to enable nodes in the network to each select individual tones within the band utilized by the network for network communications. When operating in MTM mode, only one/set of TMs may be optimal (typically the lowest noise) for each particular unidirectional/bidirectional link. After each node (device) performs an initial tone mask scanning, the nodes determine which tones are optimal for their UL communications (node to router) and for their DL communications (router to node).
The transmitter networked device may request an estimation of a channel condition by setting a selected bit in the PHY Header. The receiver networked device estimates this particular communication link between two points and chooses optimal PHY parameters. This information is sent back to the transmitter networked device as a tone map response.
Adaptive tone mapping is used to allow the receiver networked device to achieve the greatest possible throughput given the current channel conditions existing between them. To accomplish adaptive tone mapping, the receiver networked device is configured to inform the transmitter networked device which tones it should use to send data bits on, and which tones it should use to send dummy data bits that the receiver networked device will ignore. The receiver networked device may be configured to also inform the transmitter networked device how much amplification (or attenuation) it should apply to each of the tones.
FIG. 1A depicts the structure of a tone map response message frame 100 for adaptive tone mapping for a known G3 PLC network. Frame 100 includes a preamble 101, a frame control header (FCH) 102, and a tone map response data payload 103.
In IEEE P1901.2, the tone map data functions as a specific link control to avoid tones that have a low signal to noise ratio (SNR) to allow use of only “good” tones that have a relatively high SNR. In G3 FCC with a 4.6875 kHz tone spacing, each tone map defines the power level for a subband which has three adjacent tones, where the subbands each span 4.6875 kHz*3=14.0625 kHz. For example, with 72 tones in the G3 FCC band, 24 tone maps for 3 tone subbands are available to utilize.
FIG. 1B shows the tone mask response message description for a receiver networked device utilizing G3-PLC/IEEE P1901.2. TXRES is a parameter that specifies the transmit gain resolution corresponding to one gain step. TXGAIN is a parameter that specifies to the transmitter networked device the total amount of gain that it should apply to its transmitted signal. The value in this parameter specifies the total number of gain steps needed. The receiver networked device computes the received signal level and compares it to a VTARGET (pre-defined desired receive level). The power difference in dB between the two values is mapped to a 5-bit value that specifies the amount of gain increase or decrease that the transmitter network device applies to the next frame to be transmitted. A “0” in the most significant bit indicates a positive gain value, hence an increase in the transmitter gain, and a “1” indicates a negative gain value, hence a decrease in the transmitter gain. A value of TXGAIN=“0” informs the transmitter network device to use the same gain value it used for previous frame.
TM is a parameter that specifies the Tone Map. The receiver network device estimates the link quality of the channel with the granularity of the tone map subband and maps each tone map to a one-bit value. A value of “0” indicates to the transmitter network device that dummy data should be transmitted on the corresponding sub carrier while a value of “1” indicates that valid data should be transmitted on the corresponding sub-carrier.
TXCOEF is a parameter that specifies transmitter gain for each 10 kHz section of the available spectrum. The receiver network device measures the frequency-dependent attenuation of the channel and may request the transmitter network device to adjust the transmit power on sections of the spectrum that are experiencing attenuation in order to equalize the received signal. Each 14.0625 kHz section is mapped to a 4-bit value where a “0” in the most significant bit indicates a positive gain value, hence an increase in the transmitter gain is requested for that section, and a “1” indicates a negative gain value, hence a decrease in the transmitter gain is requested for that section.
In the G3-PLC/IEEE P1901.2 standard, there can be seen to be a total of 32 bits used in 8 TXCOEF fields which provide power control data for tone maps. Each TXCOEF field (4 bits) thus defines the power control level for one tone map (and thus its subband having 3 tones).